The present invention relates generally to exposure, and more particularly to an exposure method used to manufacture various devices including a semiconductor chip, a display device, a sensing device, an image pickup device, and a fine contact hole pattern for use with the micromechanics. The micromechanics applies the semiconductor IC fabrication technologies for manufactures of a fine structure, and means a sophisticated mechanical system that may operate at a micron level or the technologies for manufacturing the mechanical system.
A conventional projection exposure apparatus projects a mask (or reticle) pattern onto a wafer via a projection optics, and transfers the circuit pattern using the photolithography technology. The mask pattern can contain contact holes. Along the recent demands for fine processing to devices, the projection optics have been increasingly demanded to stably image fine contact holes. For the high-resolution pattern transfer, an optimal exposure condition, such as a mask type and an illumination condition, should be set in accordance with the pattern type. A large depth of focus (“DOF”) is necessary for a stable imaging characteristic, and the illumination condition also affects the DOF.
There are several types of contact hole patterns, such as a close and periodic contact hole array, a separated and isolated contact hole, and another isolated pattern. The contact hole array includes a matrix type in which square holes are arranged in a matrix shape, and a checker type in which respective adjacent arrays shift to each other. An actual circuit pattern mixes a matrix pattern and a checker pattern, and is referred to as a “hybrid pattern” hereinafter. There are proposed various illumination conditions suitable for the matrix pattern and the hybrid pattern. For example, an annular illumination is suitable for the hybrid pattern. In addition, a rectangular contact hole is also known. See, for example, Hochul Kim et al., “Layser Specific Illumination Optimization by Monte Carlo Method,” Optical Microlithography XVL, Anthony Yen, Editor, Proceedings of SPIE, Vol. 5040 (2003), pp. 244-250.
A known mask type covers a binary mask, a phase shift mask (“PSM”), and an attenuated-PSM. The illumination condition covers a polarization condition, and it is known that a tangential polarization is suitable for a two-beam interference, and a radial polarization is suitable for a four-beam interference. Polarization control will become important, as in an immersion exposure apparatus, etc., as a high NA scheme advances in the near future.
Other prior art include Japanese Patent Applications, Publication Nos. 2000-040656, 2003-203850, 2004-272228, 2003-318100, and 2003-233165.
A projection exposure apparatus has a resolution R optical system given by Rayleigh's formula where λ is a wavelength of a light source, and NA is a numerical aperture of a projection optics:R=k1(λ/NA)  [EQUATION 1]
Here, k1, is a constant determined by a development process, and about 0.5 to 0.7 for the normal exposure. The recent high integration of a device increasingly craves a finer transferred pattern or a higher resolution. From the above equation, a higher NA and a smaller wavelength λ are effective to the high resolution. Nevertheless, these improvements appear to reach the limits at present, and the normal exposure has difficulties in forming a contact hole pattern with 0.1 μm or smaller on a wafer.
In particular, it is difficult to image, with a sufficient DOF, a contact hole array that mixes a matrix pattern and a checker pattern. In addition, an optimal exposure condition to the checker pattern is not fully analyzed. There are demands to make the resolving characteristic better than the conventional annular illumination with a sufficient DOF for actually frequently used hybrid patterns.